The Bermuda Triangle might not be the greatest enigma lurking in the Atlantic Ocean after all.

According to a recent study featured in the journal Geophysical Research Letters, scientists may have uncovered why Bermuda remained buoyant after its volcanoes ceased activity over 30 million years ago.

Ordinarily, when volcanic activity halts, the tectonic plate tends to drift away from the deep mantle hotspot, causing the cooling crust and the volcano to gradually sink.

Yet, researchers have identified an extraordinary rock layer beneath the oceanic crust under Bermuda that acts to elevate the island.

This layer is notably thick, measuring about 12.4 miles, a level of thickness that hasn’t been observed in similar geological formations elsewhere in the world.

The team, led by seismologist William Frazer of Carnegie Science and Jeffrey Park of Yale University, analyzed seismic waves from 396 distant earthquakes, all of which were strong enough to send clean vibrations through the earth.

Using those waves and what they left behind, researchers were able to paint a vertical picture of the rocks that lay beneath Bermuda, down to about 31 miles.

The image revealed a thick layer of rock that is less dense than the rock surrounding it.

Frazer explained that typically, after the bottom of the oceanic crust, it’s expected that there would be the mantle.

“But in Bermuda, there is this other layer that is emplaced beneath the crust, within the tectonic plate that Bermuda sits on,” he told Live Science.

Bermuda sits on a oceanic swell, where the ocean crust is higher than its surroundings, rising from the ocean about 500 meters (1,640 feet) above the seafloor.

This finding suggests that the last volcanic eruption may have put mantle rock into the crust, where it froze in place and create a raft-like structure above the ocean floor.

The origin of this layer isn’t immediately clear, but Park told Brighter Side of News that “some magma may have stalled beneath the Moho instead of erupting, building a mafic pluton over time.”

“We found volatile-rich melts rising beneath Bermuda could also have efficiently depleted and modified the uppermost mantle, leaving behind a lighter residue,” he added. “Another possibility is metasomatic underplating, where hot upwelling material cracks the crust, lets seawater in, and partially serpentinizes the mantle.”

Despite 31 million years of inactivity of volcanoes there, the oceanic swell still hasn’t sunk, and while there is some debate over what may be happening beneath the surface, there have been no volcanic eruptions at the surface.

“There is still this material that is left over from the days of active volcanism under Bermuda that is helping to potentially hold it up as this area of high relief in the Atlantic Ocean,” Sarah Mazza, a geologist at Smith College in Massachusetts who was not involved in the work, told Live Science.

“The fact that we are in an area that was previously the heart of the last supercontinent is, I think, part of the story of why this is unique.”

Now, Frazer is looking into other islands around the globe to see if there are any similar layers to the one they discovered beneath Bermuda, or if it really is the only one of its kinda.

“Understanding a place like Bermuda, which is an extreme location, is important to understand places that are less extreme and gives us a sense of what are the more normal processes that happen on Earth and what are the more extreme processes that happen,” Frazer said.